1. Field of the Invention
The present invention relates to a magnetic recording medium used in an audio tape, video tape, data cartridge, floppy disc, or the like.
2. Description of the Prior Art
As a recording medium used in an audio apparatus, a video apparatus, a computer apparatus, and the like, there is widely spread a so-called paint-type magnetic recording medium for its excellence for general purpose, which recording medium has a magnetic layer prepared by painting on a non-magnetic support body a magnetic paint prepared from a magnetic powder dispersed together with a binder and various additives in a solvent and kneaded, wherein the paint is dried after applied onto the non-magnetic support body.
Various types of magnetic recording and reproduction apparatus tend to reduce the size and weight and improve the image quality as well as to increase the recording/reproduction time, which in turn requires a higher recording density in the aforementioned paint-type magnetic recording medium.
In order to improve characteristics in a high density recording region of the paint-type magnetic recording medium, firstly, selection of a magnetic powder is highly important. That is, the magnetic powder should have a high coercive force and a large saturation magnetic flux density, and should be in fine particles.
To cope with this, instead of an iron oxide magnetic powder which has been used conventionally, a ferromagnetic metal powder containing iron as a main content has come to be used as the magnetic powder contained in the aforementioned magnetic layer.
This ferromagnetic metal powder is prepared from a needle-shaped iron oxyhydroxide or iron oxide which is heated to be deoxidized in a deoxidizing gas and then a thin oxide film is formed on particle surfaces for assuring an oxide stability. The ferromagnetic metal powder thus prepared has a high coercive force, enabling to obtain a high magnetization quantity in comparison to the iron oxide magnetic powder.
Moreover, as another technique to improve characteristics in a high density recording region, there can be exemplified a technique to increase dispesibility of the magnetic paint. As the magnetic paint has a higher dispersibility, firstly, the magnetic characteristic is improved. Moreover, the rectangular ratio which is an index of particle orientation is improved as well as the residual magnetic flux density is improved. Furthermore, as the dispersability of the magnetic paint increases, the magnetic layer surface after painted has an improved flatness and smoothness, reducing a so-called spacing loss generated between the recording medium and a VTR head, which in turn improves the electromagnetic conversion characteristic.
However, in general, a ferromagnetic metal powder having a large magnetization quantity of particles tends to lower its dispersion stability when used as a paint. That is, when there is a large magnetization quantity, there arises a greater magnetic agglutination between particles and when the paint is left still or in a state near it, the particles may be precipitated, isolating the solvent. As a result, when the paint is applied for coating, it is impossible to obtain a smooth and unanimous coating, which in turn deteriorates the electromagnetic characteristic.